A leading cause of death in the United States today is coronary artery disease, in which atherosclerotic plaque causes blockages in the coronary arteries, resulting in ischemia of the heart (i.e., inadequate blood flow to the myocardium). The disease manifests itself as chest pain or angina. In 1996, approximately 7 million people suffered from angina in the United States.
One technique that has been developed to treat patients suffering from diffuse atherosclerosis, is referred to as transmyocardial revascularization (TMR). In this method, a series of channels are formed in the left ventricular wall of the heart. Typically, between 15 and 30 channels about 1 mm in diameter and preferably several millimeters deep are formed with a laser in the wall of the left ventricle to perfuse the heart muscle with blood coming directly from the inside of the left ventricle, rather than traveling through the coronary arteries. Apparatus and methods have been proposed to create those channels both percutaneously and intraoperatively (i.e., with the chest opened).
U.S. Pat. No. 5,389,096 to Aita et al. describes a catheter-based laser apparatus for use in percutaneously forming channels extending from the endocardium into the myocardium. The catheter includes a plurality of control lines for directing the tip of the catheter. The patent states that because the myocardium is more easily traversed than the epicardium, the clinician may judge the depth of the channel by sensing the pressure applied to the proximal end of the catheter. The patent does not address the problem of cardiac tamponade that might result if the clinician inadvertently perforates the heart wall, nor how ablated tissue is prevented from embolizing blood vessels. Moreover, Aita et al. rely on fluoroscopic methods to determine the location of the distal end of the catheter.
U.S. Pat. No. 5,591,159 to Taheri describes a mechanical apparatus for performing TMR involving a catheter having an end effector formed from a plurality of spring-loaded needles. The catheter first is positioned percutaneously within the left ventricle. A plunger is then released so that the needles are thrust into the endocardium. The needles form small channels that extend into the myocardium as they are withdrawn. The patent suggests that the needles may be withdrawn and advanced repetitively at different locations under fluoroscopic guidance. The patent does not appear to address how tissue is ejected from the needles between the tissue-cutting steps.
The disadvantages of the above-described previously known methods and apparatus for performing TMR are numerous and will impede the acceptance of this new treatment method. For example, percutaneous laser-based systems, such as described in the Aita et al. patent, do not provide the ability to reliably determine the depth of the channels formed by the laser and may result in perforations, nor does that system address potential embolization of the ablated tissue. Likewise, previously known mechanical systems do not address issues such as how to remove tissue cores from the needles. Neither do such previously known systems provide the capability to assess whether channel formation or durg injection at a proposed site will provide any therapeutic benefit.
U.S. Pat. No. 5,910,154 (allowed U.S. patent application Ser. No. 08/863,877, filed May 27, 1997) describes a percutaneous system for performing TMR that uses a rotating tubular cutting head disposed for reciprocation beyond the end face of a catheter. Vacuum drawn through the cutting head aspirates the severed tissue, thus reducing the risk of embolization.
It has been observed that in the device described in the foregoing patent, the distance that the cutting head extends into the tissue depends upon the degree of tortuosity imposed on the catheter when percutaneously inserting the distal end of the catheter into the left ventricle. This is so because differences in the radii of curvature of the catheter and the drive tube coupled to the cutting head can result in significant accumulated displacement of the cutting head relative to the distal endface of the catheter. This displacement effect is heightened where the tip of the catheter is articulated using a pull wire that exerts a compressive force on the catheter.
Accordingly, it would be desirable to provide apparatus and methods for percutaneously performing myocardial revascularization that enable a reciprocated cutting head to be advanced a controlled depth, independent of the degree of tortuosity imposed on the catheter.
It also would be desirable to control the location within the ventricle of a distal end of a device for percutaneously performing myocardial revascularization, both with respect to features of the ventricular walls and in relation to other channels formed by the device.
It further would be desirable to provide apparatus and methods for percutaneously performing myocardial revascularization that enable therapeutic agents, such as angiogenic growth factors, genes, or drugs to be injected into the myocardium within or adjacent to channels formed by the cutting head.
A drawback common to all of the previously known percutaneous myocardial revascularization devices is the inability to determine whether treating a proposed site, such as by forming a channel in the myocardium or by injecting drugs or angiogenic agents, would have a therapeutic effect. For example, little therapeutic benefit would be expected from forming channels or injecting drugs or angiogenic agents in heavily infarcted tissue. It would therefore be desirable to provide apparatus and methods that enable a clinician to determine whether treatment at a proposed site would be beneficial.
It still further would be desirable to provide the capability to stabilize a distal end of a device for percutaneously performing myocardial revascularization, for example, to counteract reaction forces created by the actuation of the cutting head, and to reduce transverse movement of the distal end of the device.
It also would be desirable to provide apparatus and methods for percutaneously performing myocardial revascularization that use cutting heads designed to morcellate severed tissue to enhance aspiration of the severed tissue from the treatment site.